A method and system that is portable, lightweight and economical for detecting changes in the mechanical properties of components and objectively quantifying internal characteristics would be invaluable to a broad spectrum of professionals.
In the field of dentistry, the stability of a tooth is used as an indicator of the health of the interior of the tooth, the surface of the tooth as well as surrounding structures. A tooth is not part of the alveolar bone, but is connected to the bone by the periodontal ligament. The periodontal ligament, which has a higher damping capacity than enamel, dentin, or bone, dissipates the impact energy of occlusion. Thus, periodontal structural changes lead to changes in tooth mobility. Furthermore, periodontal structural changes are also reflected in the energy damping characteristics of the periodontium.
Periodontal diseases which are very common were traditionally subjectively diagnosed by visual examination of gum inflammation, the periodontal pocket, radiographs of bone atrophy, and tooth mobility. The first attempts to objectively measure tooth mobility used static measurement procedures which investigated the static deflection of the tooth due to a pre-selected horizontal force. An early attempt at dynamic measurement procedures used a non-contact displacement transducer. However, the procedures required a stable mechanical reference system which included attachment to all the teeth except the tooth under examination.
The next advancement in the art was the Siemens Periotest as described by Lukas and Schulte and by the manufacturer, Siemens. This instrument had a handpiece which upon the pressing of a finger switch created a reproducible percussive force using a magnetic coil and a tapping rod. The deceleration of the tapping rod on impact with the tooth was measured by an accelerometer installed in the handpiece.
An analysis of the accelerometer readings indicated a correlation between the contact time and tooth mobility. This contact time was used to calculate a Periotest value which determined the appropriate category of tooth mobility. Under such a system, a Periotest value greater than or equal to thirty translated into a category III mobility which meant that the tooth could be moved with labial pressure. A Periotest value greater than or equal to twenty, but less than thirty, translated into a category II mobility which meant that mobility could be seen. A Periotest value greater than or equal to ten, but less than twenty, translated into a category I mobility which meant that mobility could be felt. A Periotest value greater than or equal to negative eight, but less than ten, translated into a category zero mobility which meant that the tooth was securely anchored.
The Siemens Periotest had several limitations. The first obstacle to accurate and reproducible readings was that the pen-shaped handpiece had to be held with the tip of its metal sleeve located between 0.5 millimeters to 2.5 millimeters from the tooth. The tip of the metal sleeve could not touch the tooth during the measurement procedure because, among other reasons, stress waves would propagate through the metal sleeve up the casing of the handpiece distorting readings. Maintaining the tip of the metal sleeve of the handpiece within the minuscule range proved a cumbersome requirement for a hand-held device. Error in judging such minuscule distances and the subsequent placement of the handpiece outside the small range of distances could be the sole cause of aberrant readings. Furthermore, variations in tip to tooth distances from measurement procedure to measurement procedure caused variations in data. Deviations placing the tip of the metal sleeve outside of the range of 0.5 millimeters to 2.5 millimeters occurred from the natural shaking of the hand which held the device or from the shaking of the device derived from the pressing of the finger switch located on the handpiece, or from the shaking of the handpiece during the measurement procedure.
The second obstacle to consistent and accurate readings was that the handpiece had to be maintained in a horizontal position. Even a small angle from the horizontal would create significant errors in the measurement due to gravity and friction affecting the kinetic energy of the tapping rod. Keeping the handpiece in a substantially horizontal position was especially difficult where the operator was holding the handpiece in the air with a focus on keeping the tip of the metal sleeve of the handpiece between 0.5 millimeters to 2.5 millimeters from the tooth and where the operator was physically pushing a finger switch on the handpiece to activate the measurement procedure. Both the distance between the tip of the sleeve and the tooth and the angle of inclination of the handpiece had to be consistently maintained during the measurement procedure and in subsequent measurement procedures in order to obtain consistent and accurate results. Moreover, the Siemens Periotest gave no warning or feedback to the operator that the handpiece was at an exorbitant angle before the commencement of the measurement procedure. Neither was the operator given any information regarding the angle at which the measurements were taken.